This invention relates to a whistle and is more particularly concerned with a dog whistle.
Dog whistles are very well known. Nevertheless, it is believed that all operating parameters have not been optimised in a single design and that there still tends to be a number of problems associated with such whistles that, as yet, have not been overcome.
Dog whistles having a single sound chamber and having a good volume of sound to be produced at a high frequency effective for dogs tend to be larger than need necessarily be the case. Additionally, such whistles need to be able to be blown quite gently for close distance work with the dog but also should be capable of being blown very hard for longer distance work. Furthermore, during the act of blowing, the sound frequency should not fluctuate unduly or otherwise this may lead to confusion on the part of the dog regarding the particular operating command.
A well known problem with this type of whistle is in achieving a compromise in the design, in order to successfully achieve both the aforementioned aims of enabling the whistle to be blown gently and effectively for close distance work without the whistle becoming very quiet when over-blown and thus losing effectiveness at long distances. Where such a whistle is designed to be very effective when blown hard it may simply fall to respond to gentle blowing and thus may be excellent for distance work but practically useless for close work.
It is an object of the present invention to at least alleviate one of the aforementioned problems associated with whistles and/or to provide a whistle which is improved in at least some respect.
According to the present invention there is provided a whistle of the kind comprising a body provided with a mouthpiece having an air passage which communicates with a sound chamber provided in the body, the chamber being provided with a vent in which is located air flow responsive means for producing a whistling sound arranged so that air blown into the chamber through the mouthpiece is directed to said means as it is vented from the chamber, characterised in that the sound chamber is shaped and dimensioned to produce sound having a narrow frequency bandwidth of less than 800 hertz.
Preferably, the sound chamber is shaped; and dimensioned to produce sound over a narrow frequency bandwidth lying in the range of about 400 to about 800 Hertz and preferably the bandwidth is about 400 Hertzxc2x120 Hertz,
Preferably, the sound chamber is generally cylindrical in shape and its diameter is within about 10 percent of the axial length of the chamber.
The overall length of the whistle is preferably about 5.3975 centimeters xc2x10.5 centimeter. The overall width or diameter of the whistle is preferably about 1.473 centimetersxc2x10.25 centimeters.
Preferably, the whistle is provided, in the air passage, with means (usually in the form of a ramp) for directing the air flow blown into the mouthpiece towards the sound producing means which is in the form of an air splitter, said air flow directing means having an operative surface which is inclined at an angle of less than 8xc2x0 to the axis of the air passage. Preferably, said angle will lie in the range of about 3xc2x0 30xe2x80x2 to about 5xc2x0 and may optimally be 4xc2x030xe2x80x2xc2x110 minutes. This angle is much reduced compared with known whistles of the kind referred to and generally should enable compression of the air blown into the mouthpiece to be reduced as it impinges on the air splitter. This is important as it guarantees the highest possible air pressure on the air splitter. Additionally, a more even distribution of air may be provided with the added advantage of preventing some frequency fluctuation.
Preferably, the air splitter is formed by an edge of a surface arranged at an angle greater than 38xc2x0 with respect to a transverse plane perpendicular to the axis of the sound chamber. Preferably, this angle lies within a range of about 45xc2x0 to about 55xc2x0 and may optimally be 55xc2x0. Increasing the said angle of the air splitter to above 38xc2x0 may provide a marked improvement in performance over known whistles, effectively reducing any back pressure In the sound chamber which can create stalling and silencing of the whistle under pressure.
Where air flow directing means is provided as aforesaid, the operative surface of such means may be provided at the end thereof adjacent the sound chamber with a face which is inclined to the axis of the air passage at an angle within the range of about 30xc2x0 to about 60xc2x0. Optimally, this angle may be 45xc2x0xc2x15xc2x0. Correctly selecting this angle may create a more constant frequency throughout the same range of the whistle.
The length of said face may be 0.127 centimetersxc2x10.05 centimeters. Any length longer than this would cause stalling of the whistle through the build-up of back pressure while any shorter length would allow the frequency to vary as the blowing pressure is varied. The overall length of the operative surface of the air directing means and this face may be of the order of 1.98 centimeters.